Filter system for hydraulic circuit

ABSTRACT

A hydraulic circuit including a reservoir, a pump for withdrawing fluid therefrom and for directing it under pressure through a control valve and to a hydraulic motor and means for directing return fluid back to the reservoir and through a filter which is disposed entirely within the reservoir. The filter has no external fluidtight housing and fluid is filtered by passing outwardly through a hollow filter unit so that the filtered fluid passes at relatively low pressure and velocity into the body of fluid in the reservoir to avoid agitating and aeration of the fluid supply therein.

United States Patent Inventor Roger A. Rice Joliet, Ill. Appl. No. 837,529 Filed June 30, I969 Patented Mar. 30, 1971 Assignee Caterpillar Tractor Co. Peoria, Ill.

FILTER SYSTEM FOR HYDRAULIC CIRCUIT 9 Claims, 3 Drawing Figs.

U.S.Cl 210/130, 210/172,210/249,210/416 Int. Cl 3010,35/ 14 B01d35/02 FieldofSearch 210/130,

[56] References Cited UNITED STATES PATENTS 2,747,743 5/1956 Talak 210/130 3,214,023 10/1965 Donner 210/172 Primary Examiner-Frank A. Spear, Jr. AttorneyFryer, Tjensvold, Feix, Phillips & Lempio FILTER SYSTEM FOR HYDRAULIC CIRCUIT Filters for oil in hydraulic systems are generally made with a housing having inlet and outlet openings to which conduits may be attached. Generally, the fluid to be filtered is directed into the housing exteriorally of a hollow filter unit then passes through the unit and from the interior thereof to the outlet opening. Since the fluid goes through the filter at relatively high pressure, it is ejected through theoutlet opening and conduit attached thereto rather forcibly and at high velocity into the reservoir to which it is returned for further use. This often causes aeration of the fluid in the reservoir and air becomes entrained in fluid which is withdrawn by a pump and directed to a fluid motor or the like causing cavitation in the pump and unsatisfactory operation of the motor. These disadvantages are overcome by the present invention which is directed to a hydraulic circuit in which the filter has no ordinary housing, is placed interiorally of a reservoir and ejects fluid from its exterior surface under relatively low pressure and low velocity. The invention is disclosed in detail in the accompanying drawing and described by reference to the drawing in the following specification.

In the drawing:

FIG. 1 is a schematic view of a hydraulic circuit embodying the present invention;

FIG. 2 is a sectional view through the filter shown in FIG. 1; and

FIG. 3 is a similar view of a slightly modified form of the filter.

The schematic illustration of FIG. I shows a tank which serves as a reservoir for hydraulic fluid. The fluid is withdrawn from the tank through a line 12 and by a pump 14 which directs it through a valve 16 and selectively to opposite ends of a hydraulic motor, shown as a jack 118, by way of lines 20 and 22. The valve 16 is illustrated as a spool-type valve which may be operated either manually or by the force of fluid in a pilot system. Neither of such actuating means are illustrated herein since they are conventional and form no part of the present invention.

Valve 16 also serves to receive return fluid from the hydraulic motor and direct it to a filter and back into the tank. For example, fluid under pressure going to either end of the motor 1a through line 20 or line 22 will move a piston 24 in the motor and cause ejection of fluid from the opposite end through the opposite line. This return fluid will be directed through a line 26 within the tank, through a filter generally indicated at 28 and thence returned directly to the body of fluid within the tank.

The filter is illustrated in FIG. 2 as having a hollow cylindrical unit of filter material 32 encased between inner and outer perforated metal sleeves 34 and 36 respectively. An end closure 38 at one end of the filter is secured against a wall of the tank at an opening therein by means of cap screws such as shown at 40. A centrally disposed screw 42 extends part of the way through the filter and threadedly engages a tubular inlet fitting 44 to draw an end closure 46 against the opposite endof the filter. The end closure 46 also serves as a spring chamber for a relief valve presently to be described.

In operation, oil returned from the hydraulic motor and through the valve 16 is directed into the filter by line 26 and enters the hollow filter unit through perforations 49 and the tubular member 44. As oil passes through the filter unit it emerges through the perforations in the outer cylindrical .member 36. These perforations are large and numerous providing a large flow path so that the pressure and velocity are greatly reduced when compared with conventional filters where the outflow line would be approximately the size of the tered liquid will be admitted to the tank through a relief line 50. A conventional relief valve shown at 52 is associated with a control valve 16 for relieving excesspump pressure.

A slightly modified form of the filter of FIG. 2 is illustrated in FIG. 3 wherein an end closure 38 replaces the end closure 38 of FIG. 2 and receives two or more long cap screws 42 which are threaded into the end closure 46' at the opposite end of the filter for retaining it in place. With this modified construction, fluid from the inlet conduit 26 is free to flow straight through the fitting 44' without the obstruction shown in FIG. 2.

lclaim:

ll. In a hydraulic circuit which includes a reservoir, a pump for withdrawing hydraulic fluid from the reservoir, a motor to which the fluid may be directed from the pump and a return line from the motor to the reservoir, wherein the improvement comprises a filter disposed within the reservoir and operably associated with the end of the return line, said filter having an element of generally cylindrical configuration with a hollow center, first and second closure means at either end of the element, means to introduce fluid to be filtered through said first closure means, the outer surface of the filter element being exposed to the interior of the reservoir, and relief valve means associated with said first closure means for communicating said hollow center of said filter element with said reservoir when excessive pressure buildup occurs in said filter.

2. The improvement of claim I in which the filter has no external housing and fluid passing through the filter element flows directly into the reservoir.

3. The improvement of claim 1 in which a wall of the reservoir is provided with an opening, means securing an end of the filter to the wall to close said opening, a closure for the opposite end of the filter, and threaded securing means extending through said first end and into the closure at the opposite end.

4. The improvement of claim 1 wherein said relief valve means comprises a relief valve in the form of a valve element and a spring biasing said valve element against the end of said filter element associated with said first closure means.

5. The improvement of claim 4 wherein said means to introduce fluid through the first closure means comprises a tubular member and wherein said valve element is slidable on said tubular member.

6. The improvement of claim 5 wherein said tubular member extends into the hollow center of said element, thereby communicating fluid to said hollow center.

7. The improvement of claim 6 further including means closing the end of tubular element which extends into said hollow center and at least one perforation in the side of said tubular member intercommunicating the interior of said tubular member with said hollow center.

8. The improvement of claim 7 wherein said means closing the end of tubular element comprises a centrally disposed screw extending part way through the filter and threadably engaging said tubular element.

9. The improvement of claim 4 further including a relief line intercommunicating the spring side of said relief valve element with the interior of said reservoir. 

1. In a hydraulic circuit which includes a reservoir, a pump for withdrawing hydraulic fluid from the reservoir, a motor to which the fluid may be directed from the pump and a return line from the motor to the reservoir, wherein the improvement comprises a filter disposed within the reservoir and operably associated with the end of the return line, said filter having an element of generally cylindrical configuration with a hollow center, first and second closure means at either end of the element, means to introduce fluid to be filtered through said first closure means, the outer surface of the filter element being exposed to the interior of the reservoir, and relief valve means associated with said first closure means for communicating said hollow center of said filter element with said reservoir when excessive pressure buildup occurs in said filter.
 2. The improvement of claim 1 in which the filter has no external housing and fluid passing through the filter element flows directly into the reservoir.
 3. The improvement of claim 1 in which a wall of the reservoir is provided with an opening, means securing an end of the filter to the wall to close said opening, a closure for the opposite end of the filter, and threaded securing means extending through said first end and into the closure at the opposite end.
 4. The improvement of claim 1 wherein said relief valve means comprises a relief valve in the form of a valve element and a spring biasing said valve element against the end of said filter element associated with said first closure means.
 5. The improvement of claim 4 wherein said means to introduce fluid through the first closure means comprises a tubular member and wherein said valve element is slidable on said tubular member.
 6. The improvement of claim 5 wherein said tubular member extends into the hollow center of said element, thereby communicating fluid to said hollow center.
 7. The improvement of claim 6 further including means closing the end of tubular element which extends into said hollow center and at least one perforation in the side of said tubular member intercommunicating the interior of said tubular Member with said hollow center.
 8. The improvement of claim 7 wherein said means closing the end of tubular element comprises a centrally disposed screw extending part way through the filter and threadably engaging said tubular element.
 9. The improvement of claim 4 further including a relief line intercommunicating the spring side of said relief valve element with the interior of said reservoir. 